1. Field of the Invention
The present invention relates to a sheet feeding device for feeding an uppermost sheet of a stack of sheets which is attracted under suction by a suction cup or pad to a delivery mechanism to deliver the uppermost sheet to a next station.
2. Description of the Related Art
In order to deliver sheets such as unexposed photographic light-sensitive mediums which have been stacked and accommodated, to an exposure station or to deliver sheets after images have been exposed thereon to a developing machine, there is employed a sheet feeding device for taking out the sheets one by one so as to deliver to a desired station.
In the sheet feeding device, stacked sheets are first loaded in a given sheet placement position in a supply magazine. Thereafter, an uppermost sheet of stacked sheets is attracted under suction by a suction cup or pad (separating means) so as to withdraw from the sheet placement position. The uppermost sheet thus withdrawn is delivered from the suction pad to a delivery mechanism, from which the sheet is supplied to an exposure device, an automatic photographic processors, etc.
A detector is disposed in a stop position corresponding to a sheet delivery position, of the suction pad. Alternatively, there is disposed an arrangement for mechanically stopping the suction pad from moving. Under this condition, the uppermost sheet, which has been attracted and held under suction by the suction pad, is fed to the stop position at a uniform speed or at a uniform angular velocity, followed by delivery of the sheet to the delivery mechanism.
There is now demand for carrying out a sheet feeding process at a high speed. In order to meet this demand, it is necessary to move the suction pad with the uppermost sheet attracted thereto to its stop position at a high speed. It is, however, hard to reliably stop the suction pad while being moved at a high speed at its stop position. The suction pad tends to move beyond the stop position. Therefore, the uppermost sheet is subjected to scratches and fog under pressure when it is inserted between a pair of rollers serving as a delivery mechanism.
In the sheet feeding device, when the delivery mechanism receives the uppermost sheet from the suction pad, the delivery mechanism comprising a pair of delivery rollers, a drum, delivery belts, etc. is driven synchronism with a travel speed of the suction pad. In addition, the delivery mechanism is activated in synchronism with sheet conveying speeds of an exposure device or an automatic photographic processor, etc. when the uppermost sheet is delivered to the exposure device, the automatic photographic processor, etc. from the delivery mechanism.
A drive mechanism of the sheet feeding device is normally activated by an induction motor, and its rotational speed is adjusted in analog form by operating a control knob or the like of a speed controller electrically connected to the induction motor. In particular, when the sheet conveying speed of the succeeding station such as the exposure device, the automatic photographic processor, etc. ranges from a relatively low speed to a high speed, it is, however, very hard to adjust the sheet delivery speed in analog form so as to meet the conveying speed of the succeeding station, because the rotational speed of the induction motor is adjusted in analog form as described above. There are often situations in which, for example, there is an appreciable difference in sheet (e.g., photographic film) conveying speeds depending on the types of developing machines to be connected or there is an appreciable difference in sheet conveying speeds even in a single developing machine if a gear is replaced.
There is also a slight mechanical difference between the actual sheet conveying speed and the nominal sheet conveying speed of each automatic photographic processor or the like connected as the succeeding station. It is therefore necessary to fine-adjust such a mechanical difference in order to accurately synchronize both speeds with each other.